S+
S
CL
1300
1400
1525 1565 1600
Expand the total bandwidth
utilize dispersion shifted fiber without the FWM penalty
C-Band v.s. L-Band
6.3dB/mw gain coefficient and max power conversion efficiency (PCE) 77.2% with 1.48 pump at 1.55 band
Power and SNR Fluctuations
Optical Attenuation Compensation
Every EDFA needs compensation Same idea applies for pump power
compensation
Control Channel Method
Penalty for higher filter loss is higher NF and lower output power
Long-Period Fiber Grating Filter
Index grating period ~100mm provides coupling between the core and cladding modes
gain coefficient is smaller for 1.58 band due to smaller stimulated cross section
PCE is higher in the 1.55 band. This is because 1.58 amplification occurs from the 1.55 ASE generated from 1.48 pump
• High power pumps are expeቤተ መጻሕፍቲ ባይዱsive at the wavelengths of interest
喇曼散射
光纤喇曼增益系数
传输方程（forward pumping）
dI s dz
gR Aeff
I p Is s Is
dI p dz
p s
gR Aeff
Gain Spectrum
Population at different levels are different resulting gain dependence on wavelength
Different pumping level has different spectrum
Non-Uniform Gain Accumulation
Raman Amplifier
Advantages
Disadvantages
• SRS effect is present in all fibres
• Fast response time
• Gain at any wavelength
• High pump powers required
• Low NF due to low ASE
Hybrid EDFA at 1.55um
gain excursion less than 0.9 dB
Acousto-Optic Tunable Filter
Active AOTF
Active AOTF
Gain tilt due to pump power change Active gain flattening (<0.7dB) independent
insensitive Low distortion and low noise (NF<5dB)
Erbium Doped Fiber Amplifier
EXCITED STATE
METASTABLE STATE
Pump Photon 980 or 1480 nm
SIGNAL PHOTON 1550 nm
LPG Design and Result
Over 40nm gain flattened
Hybrid EDFA at 1.55um
By optimizing the length of each fiber, gain flatness and low noise can be achieved
1.1 dB over 30 nm
Fluoride-Based EDFA
Naturally Flat. Pumped only at 1480 nm Noisier, brittle, difficult to splice with typical fiber
Passive Gain Equalization
Gain Flattening
Passive equalization
Pre-equalize the input signal Add dopant: fluoride based EDFA Broadband filter Hybrid pump
Active equalization
光放大器基本原理和特性
Outline
Introduction Erbium-doped fiber amplifier (EDFA) Raman Amplifier (RA) Semiconductor Optical Amplifier (SOA)
Introduction
一、光电中继器（O-E-O） 装置复杂、耗能多、不能同时放大多个波长信道，在WDM 系统中复杂性和成本倍增，可实现1R、2R、3R中继
transient happens in s to ms transient penalty depends on data rate,
number of EDFAs and number of channels. power increase degrades performance due to
one.
EDFA Transient Dynamics
plot
Single EDFA
For single EDFA, transient response is slow (on the order of ms)
Cascade EDFA
The transient time reduces to s range for large number of cascading EDFAs.
Acousto-Optic Tunable Filter (AOTF)
Gain flatness
Silica fiber of 20 dB gain
1dB variation over 20nm, 2.5 dB over 30nm
Fluoride fiber of 20dB gain
I pIs pI p
泵浦源（一）
复用半导体泵浦激光器
偏振合波器
LD
复
光纤光栅
用
泵浦源（二）
喇曼光纤激光器
LD泵浦双包层掺杂光纤激光器 固体激光器泵浦光纤激光器 环形腔光纤激光器
of input power with 35nm bandwidth
EDFA Gain Transient
Channel turn-on, re-routing, network reconfiguration, link failure….
Gain Transient
Power may become too high (nonlinearity) or too low (degrade SNR) when add/drop channels
boost the recieved signals
LAN amplifiers
compensate distribution losses in local-area networks
Recent Progress and Requirements
• Broad Band • High Gain • Flat BW • Low Noise • High Power • High Reliability • Low Cost • Compactness
EDFA
Erbium-doped fiber amplifier 掺铒光纤放大器
EDFA
EDFA has revolutionized optical communications
All optical and fiber compatible Wide bandwidth, 20~70 nm High gain, 20~40 dB High output power, >200mW Bit rate, modulation format, power and wavelength
SPM
Gain Saturation
G 1 Psat ln Gmax Pin G
Output saturation power is defined as the output power when gain drops by 3dB
Power amplifiers usually operate at saturation. Saturation gain is lower than the unsaturated
二、光放大器（O-O） 多波长放大、低成本，只能实现1R中继
三、光放大器类型：掺杂光纤放大器（EDFA、PDFA） 半导体光放大器（SOA） 非线性光纤放大器（FRA、FBA） 光纤参量放大器（FPA）
四、发展历程： 80年代中、后期SOA的研究为主；90年代EDFA获得巨大 成功，成为光纤通信系统必不可少的器件